1. Field of the Invention
This invention relates in general to the field of data storage devices such as disk drives having thin film magnetic disks. More particularly the invention relates to high moment films, their inherent problems with magnetic anisotropy loss during HA anneal processes, and their use in Giant Magnetoresistive (GMR) heads.
2. Description of Related Art
As magnetic recording density increases, materials with higher saturation magnetization, 4πM5, are required in the write head to write higher coercivity media. At the same time, the data rate is increasing, making domain control more critical in the write head. Such domain control is difficult, however, in state of the art GMR heads because the fabrication process for GMR sensors requires annealing with a magnetic field applied perpendicular to the easy axis (EA) of the pole materials in the write head. Hard axis annealing, required in GMR wafer processing, degrades magnetic anisotropy in Fe-based high moment films. The resulting domain structures are unfavorable for efficient writing in a yoke/pole application and sensor stability in a shield application.
Plated films, such as Ni80Fe20, Ni45Fe55, and high moment CoNiFe alloys, lose all or nearly all of their anisotropy in these hard axis (HA) annealing steps. As a result, the domains in the poles do not form in the desired orientation parallel to the air bearing surface (ABS). Laminated Fe—M—N (M=1-5 at. % Al, Zr, Ta) films are known in the art and can be made with high 4πM5=19-20 kG. As with plated films, however, these films are known to lose anisotropy during HA annealing and in many cases to switch their easy axis direction.
The problem of magnetic anisotropy loss in Fe—N based high moment films has been identified in the literature, e.g., in Fe—Ta—N films studied at the University of Alabama. The published literature states that such behavior is intrinsic to this class of materials. Previous RF magnetron processes involving N2 and N2O, produce films that resist hard axis annealing. Also, RF processes tend to be difficult to transfer to multiple tools. On the other hand, work with simple DC magnetron deposition has produced films that have poorly defined anisotropy. DC magnetron films are also extremely sensitive to process conditions and have properties that are harder to control than those of RF films.